This invention relates to an ink jet recording head using a piezoelectric thin film for an ink jet drive source and a manufacturing method therefor. Further, it relates to an ink jet recorder using the recording head.
There is a piezoelectric ink jet recording head using PZT elements comprising PZT of piezoelectric elements as electro-mechanical transducer elements of liquid or ink jet drive source. This type of the piezoelectric ink jet recording head is proposed in, for example, Japanese Patent Application Laid-Open No. Hei 5-286131.
This conventional head will be discussed with reference to FIG. 10. Another conventional head is shown in FIG. 42. The recording head has separate ink passages (ink pressure chambers) 9 on a head base 1 and a diaphragm 8 so as to cover the separate ink passages 9. A common electrode (lower electrode) 3 is formed so that it is attached to the diaphragm 8, and PZT elements 4 are placed so as to reach the tops of the separate ink passages 9, a separate electrode (upper electrode) 5 being placed on one face of the PZT element.
In the recording head, an electric field is applied to the PZT element for displacing the same, thereby pushing out ink in the separate ink passage from a nozzle of the separate ink passage.
The sequence of events for the inventor to diligently study conventional ink jet recording heads and reach the invention will be discussed.
In the conventional ink jet recording head previously described, a pattern shift occurs between the PZT element and the upper electrode and even if they are patterned with the same pattern, it is feared that a leak between the upper electrode and the common electrode will occur due to a pattern shift between the PZT element and the upper electrode.
Then, to attempt to avoid this problem, it becomes necessary to make the upper electrode pattern smaller than the PZT element pattern. That is, the form shown in FIG. 10 is changed to that in FIG. 11. In doing so, it is feared that the electric field on the upper electrode 5 side will not be applied to the piezoelectric part where the upper electrode does not exist, worsening the efficiency for jetting ink.
That is, the part of the piezoelectric body, to which no electric field is applied, not deformed restrains the deformed part, lessening displacement of the entire piezoelectric body. If the upper electrode is not positioned at the width direction center of the piezoelectric film, namely, the widths of the undeformed parts of the piezoelectric film at the left xcex94X1 and right xcex94X2 shown in the FIG. 43 differ (xcex94X1 greater than xcex94X2, for instance), the piezoelectric film deformation becomes distorted, lowering the jet characteristic and stability.
Then, to solve the problem, the inventor forms the piezoelectric body as a thin film and etches the piezoelectric thin film and separate electrodes at the same time, for example, by using a photolithography technique, thereby providing a new ink jet recording head with the piezoelectric thin film and electrodes patterned in the same shape.
On the other hand, to jet ink equal to or more than ink with an ink jet using a bulk piezoelectric body for piezoelectric thin film of thin PZT element, it is desirable to form a PZT thin film having an extremely large piezoelectric constant more than bulk PZT for deforming a diaphragm.
Generally, the piezoelectric constant of the PZT thin film is only a half to a third of the piezoelectric constant of bulk PZT and if only PZT elements differ and other design values are the same, it is difficult to use the PZT thin film to jet ink more than ink with bulk PZT.
A method of increasing the PZT thin film formation area is available to enable use of a PZT thin film having a small piezoelectric constant. According to this method, an amount of ink required for printing can be jetted, but if the PZT thin film area increases, ink jet recording head cannot be formed in high density and high-definition print quality cannot be provided.
It is therefore an object of the invention to provide an ink jet recording head capable of effectively applying an electric field to a piezoelectric thin film and stably providing a sufficient jet characteristic with no pattern shift between the piezoelectric thin film and an electrode.
It is another object of the invention to provide a high-definition, high-accuracy ink jet recording head while providing a sufficient ink jet amount in a small diaphragm area.
It is a further object of the invention to provide a method for manufacturing the ink jet recording head.
It is another object of the invention to provide an ink jet recorder and an ink jet printer system each comprising the recording head.
To these ends, according to one aspect of the invention, there is provided an ink jet recording head comprising a nozzle orifice for jetting ink, an ink chamber for supplying ink to the nozzle orifice, a diaphragm for pressurizing ink in the ink chamber, a piezoelectric thin film serving as a pressurization source for the diaphragm, and an electrode for the piezoelectric thin film wherein the piezoelectric thin film and the electrode are patterned to the same shape. According to the invention, the piezoelectric thin film and the electrode are patterned in the same step, so that a pattern shift does not occur between the piezoelectric thin film and the electrode and an electric field can be effectively applied to the piezoelectric thin film, stably providing a sufficient jet characteristic.
Patterning the piezoelectric thin film and the electrode to the same shape preferably can be accomplished by etching them at the same time.
In a preferred form, the piezoelectric thin film is a thin film 0.3-5 xcexcm thick formed by a sol-gel method or a sputtering method.
Further, in the present invention, the piezoelectric thin film is formed via the diaphragm on the ink chamber not reaching the outside of the ink chamber and that the portion of the diaphragm in the area not attached to the piezoelectric thin film is thinner than the portion of the diaphragm in the area attached to the piezoelectric thin film. Therefore, the diaphragm portion in the area not attached to the piezoelectric thin film easily bends, so that a high-definition, high-accuracy ink jet recording head can be provided while providing a sufficient ink jet amount in a small diaphragm area without increasing the piezoelectric thin film area.
Preferably, the electrode comprises a common electrode to a pattern of the piezoelectric thin films and a separate electrode for the separate piezoelectric thin film, the diaphragm comprises the common electrode and an insulating film, and the portion of the common electrode not attached to the piezoelectric thin film is thinner than the portion of the common electrode attached to the piezoelectric thin film. Alternatively, the electrode comprises a common electrode to a pattern of the piezoelectric thin films and a separate electrode for the separate piezoelectric thin film and the diaphragm is made of the common electrode.
Furthermore, the electrode comprises a lower electrode and an upper electrode for separate piezoelectric thin films, the diaphragm comprises the lower electrode and an insulating film facing the ink pool, and the lower electrode is formed and attached only to areas of piezoelectric thin films. Alternatively, the area of the insulating film where the piezoelectric thin film is not formed is thinner than the area of the insulating film where the piezoelectric thin film is formed.
According to the invention, there is provided an ink jet recorder comprising the ink jet recording head.
According to another aspect of the invention, there is provided a method for manufacturing an ink jet recording head, comprising a first step of forming an ink chamber for supplying ink to a nozzle orifice for jetting ink on a substrate, a second step of forming on the substrate a diaphragm for pressurizing ink in the ink chamber, a piezoelectric thin film serving as a pressurization source for the diaphragm, and an electrode for the piezoelectric thin film in sequence, and a third step of patterning the piezoelectric thin film and the electrode.
Preferably, the second step provides the electrode comprising a common electrode to a pattern of the piezoelectric thin films and a separate electrode for the separate piezoelectric thin film and makes a projection area of the separate electrode opposite to a surface of the common electrode the same as an area of surface of the separate piezoelectric thin film. The third step dry-etches the separate electrode and the piezoelectric thin film in batch. Preferably, the dry etching is an ion milling method or a reactive ion etching method.
Preferably, the second step comprises the steps of forming and attaching an insulating film onto a surface of the substrate, forming and attaching a first electrode, forming and attaching a piezoelectric thin film onto the electrode, and forming and attaching a second electrode onto the piezoelectric thin film and the third step comprises the steps of patterning a resist on the second electrode by photolithography, patterning the second electrode and the piezoelectric thin film with the resist as a mask by a first etching method, and thinning the first electrode by a second etching method.